upper inlet manifold gasket

what does this gasket do, does it stop water getting out of the lower v block, or air getting into the system. just wondering what would happen if that gasket was not sealed properly
just in case you dont know which gasket i mean, its the one with 8 holes holding the 8 trumpets in place.

seals both housings together to stop air leaks primarily, airs supposed to enter via afm